Traveling-wave tubes are capable of amplifying and generating microwave signals over a considerable frequency range (e.g., 1-90 GHz) with relatively high output powers (e.g., >10 megawatts), relatively large signal gains (e.g., 60 dB), and over relatively broad bandwidths (e.g., >10%).
In a traveling-wave tube, an electron gun generates a beam of electrons that are directed through a slow-wave structure and collected by a collector. The electron gun generates the beam of electrons by creating an electrical potential between a cathode and an anode. Electrons emitted from the cathode are accelerated towards the anode by the electrical potential between the anode and cathode. The slow-wave structure generally comprises either a helical conductor or a coupled cavity circuit with signal input and output ports located at opposite ends of the structure. The electron beam is directed into an opening of the slow-wave structure, through the slow-wave structure, and out another opening in the slow-wave structure. A beam-focusing structure surrounding the slow-wave structure creates an axial magnetic field that contains the electron beam within the slow-wave structure.
A microwave signal applied to one of the ports propagates along the slow-wave structure to the other port at a projected axial velocity that is considerably less than the free space speed of light. With the velocity of the electron beam adjusted to be similar to the projected axial velocity of the microwave signal propagating along the slow-wave structure, the fields of the microwave signal and electron beam interact with one another so as to transfer energy from the electron beam to the microwave signal, thereby amplifying the microwave signal.
A traveling-wave tube may be used as an amplifier by coupling a microwave signal to the signal input port of the slow-wave structure. The microwave signal propagates towards the signal output port in the same direction as the electron beam and becomes amplified by extracting energy from the electron beam. As a result of this energy exchange, the electron beam loses energy which reduces the velocity of the electron beam.
During operation, the power supply of a traveling-wave tube system stores a large amount of energy. When the traveling-wave tube system is turned off, the system must dissipate the energy without damaging components of the traveling-wave tube system. This problem is more difficult as newer traveling-wave tube systems are developed that require greater amounts of energy to operate. In addition, traveling-wave tube systems that employ components using more delicate structures (e.g., helical structures fabricated using fine gage wires) are more prone to damage when the traveling-wave tube system is turned off and the energy stored in the system must be dissipated.
A need therefore exists for systems and methods for providing traveling-wave tube systems that dissipate energy stored in the system in a manner that minimizes the risk that components of the system will be damaged.